The present invention relates to a beam forming method from receiving signals of ultrasonic waves and an apparatus therefore in an ultrasonic imaging system, in particular, in an electronic scanning type ultrasonic imaging system.
As a receiving beam former circuit in a conventional ultrasonic imaging system, for example, a beam former circuit using delay means which performs its delaying operation by sampling is known as disclosed in Japanese Patent Unexamined Publication No. 61-76142.
In the above-mentioned related technique, there has been a problem of reduction in S/N due to occurrence of delay switching noise or due to occurrence of periodic noise. The delay switching noise is a kind of switching noise due to dynamic focusing in which the quantity of delay of a reception echo signal is switched by changing a focal position. On the other hand, the periodic noise (which becomes a "fixed pattern" noise in displayed picture) is generated in so-called parallel sampling in which the respective sampling timings of a plurality of parallelly-connected switched capacitors are shifted relative to each other to thereby make the sampling frequency high.